Thermal switch



Sept. 27, 1927. 1,643,792

B. H. SMITH THERMAL SWITCH Filed Jan. 24. 1921 46 .INVENTOR ii BQ/yaM/YIHASM/T/I BY 45 AiTORNEY Patented Sept. 27, 1927.

UNITED STATES BENJAMIN n. smrrir, or wrrxrnsnnne,

PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTUIEtING COMPANY, A CORPORATION OF IPENNSYL- VANLA.

THERMAL swlncn.

Application filed Janaury 24, 1921. Serial No. 439,403.

My invention relates to electric switches and particularly to control switches of the thermally-actuated type.

One of the objects of the invention is the provision of simple and efi'ective means for controlling an electrical circuit through variations in the temperature of any glven ob- 'ect.

3 Another object of the invention is the provision of a simple and compact form of apparatus whereby a snap movement of the movable contact member may be secured.

Still another object is the provision of an improved form of contacting tip whereby the objections incident to the use of cooperating contact' members of like metal are avoided. i As shown in the accompanying drawing:

Figure 1 is a plan view of a switch designed in accordance with my unvent on;

Fig. 2 is a sectional view thereof, in elevation; I

Figs. 3 and t are plan and elevational views, respectively, of a connecting member: Figs. 5 and 6 are plan and elevational views, respectively, of the movable contact member;

Fig. 7 is a plan view of the magnet employed, and a I Fig. 8 is a diagrammatic illustration of a type of system in which the swltch is designed to be employed. The switch is enclosed in a box 8 having a cover plate 9 and provided with an opening 10 into which is threaded a conduit carrying wires (not shown) for attachment to the terminals. An opening 11 may also be provided in the bottom of the box to permit the thermal medium to circulate through the switch box.

The switch parts proper are secured to a porcelain base 12 "having a depression 120: therein in one it'ace. as are also terminals 13, 14 and 15. A bushing 16 extends through the base and serves as a bearing for a shaft 17 that. is actuated by a handle 18. The

lower end of the shaft is riveted to a bracket 19 and serves to support said bracket andspindle20 is provided with a hub 22 rigidly 56 secured thereto. A movable contact member 23 is also rigidly secured to the hub 22, by a press fit or otherwise, and a connector" bar 24that leads from the terminal 13 extends over the upper end of the bracket 19 and is supported thereby, being provided with a hole 25, through which the shaft 17 extends, and with another hole 26 through which an upwardly-extending portion 27 of the movable contact member 23 extends. The opening 26 is sufficiently large to permit of reciprocatory'movement of the movable contact member 23 about a point 28. The end of the member 23 opposite the portion 27 is enlarged to provide a counterbalance, thereby ensuring proper operation irrespective of the angular position of the device relatively to a horizontal plane.

Referring particularly to Figs. 5 and 6, the movable contact member 23 is provided, at-its upper end, with a hole intowhich a contact tip 29 of silver wire or similar material is riveted. The contact member 23 and the stationary contact members 30 and 31 are preferably of steel and the contact tip 29, being of silver or similar material having good conductivity, permits the body of the movable contact member to be made of a comparativ'ely cheap material without sacrifice of current-conducting qualities and also avoids the tendency of two contact members to freeze when such members are made of like material. It will be seen that the stationary contact members 30. and 31 are adjustable with respect to theanovable contact member 23. x A horse-shoe magnet 33 is located in the depression 12a and is so positioned that its. ends lie beneath the stationary contact mem- W bers 30 and 31, such ends being spaced apart to permitof movement of the contact member 23 back and forth between the stationary contact members 30 and 31. The movable contact member 23 is acted upon by the poles m0 of the magnet to more firmly hold it in engagement with either of the contact members 30 and 31,'to prevent vibration of the movable contact member and to cause it to move with a snap action when actuated by the thermal element to be hereinafter described. A bimetallic coil spring 32 has one end thereof secured to the hub 22 and its other end secured to the bracket 19. As the coils of the spring 32 expand or contract, through changes in temperature, and the shaft 17 has a tight fit in the bushings 16, the spindle 20 will be rotated, carrying with it the hub 22 and the movable contact member 23, causing such movable contact member to make and break engagement with the stationary contact members 30 and 31, respectively.

It will be obvious that, when the tension of the spring is sufii'cient to overcome the attraction of either of the poles of the magnet 33, it will move away from such pole and toward the opposite pole with a snap movement. The contact member 23 is prevented from making actual engagement with the poles of the magnet 33 by reason of the contact tip 29 coming into engagement with the contact members 30 and 31 during its respective movements.

The connecting member 24 is insulated in any desired manner, as by a plate 35 of any suitable insulating material, from the ends of the magnet 33, and current is conducted from either of the terminals 14 and 15 through the movable contact member 23 and parts 22' and 19 to the connecting member 24 and thence to the terminal 13.

The magnet 33 is secured to the porcelain base by a pair of screws 37 and a dial 38 is provided with a scale so that the handle 18 may be positioned to vary the adjustment of the spring and cause it to actuate the movable contact member 23 at any desired predetermined temperature.

The porcelain base is secured to the cover plate 9 by a pair of bolts 39, so that, when the cover is removed, the switch parts carried thereby are conveniently accessible for inspection and repairs.

One form of apparatus with which my switch is designed to be used is illustrated in Fig. 8, wherein a circuit 40 is utilized to heat a body of liquid in aftank 41. and the circuit through such tank is controlled by a switch 42 that is actuated by a motor 43 to make and break a circuit across terminals 44 and 45.

In practice, the switch box 8 is mounted in such relation to the tank 41 as to be readily afi'ect-ed by changes in the temperature of the liquid contained in the tank.

The movable contact member 23 is normally in engagement with one of the terminals 14 and 15. When the switch 42 closes the circuit through the terminals 44 and 45, the movable contact member 23 is in engagement With the stationary contact member 15, and the circuit through the control switch is broken. If now, the temperature in the tank 41 rises beyond a predetermined degree, the thermal spring 32 willbe actuated to cause the movable contact member 23 to move into engagement with the terminal 14. The conreverse direction and cause the contact member 23 to again engage the terminal 15 to actuate the motor and thus again com lete the main circuit through the termina s 44 and 45.

It will be apparent that the control switch may be used in connection with any one of many different types of heaters, and that, instead of operating to control a motor circuit directly, it ma be utilized to o erate through a relay. arious other mo ifications may be made in the construction of the apparatus and in the method of its application without departing from the scope of the inventiomas defined in the accompanying claims.

I claim as my invention:

1. In combination, in an electric switch, a base, of electric-insulating material havin a depression in one surface thereof, an a justable yoke member of U-shape located in said depression, a spindle pivotally supported bet-ween the arms thereof, a bimetallic spring having one end connected to the yoke and its other end connected to the spindle, a support for the yoke extending through the base, a counterbalanced movable contact member carried by the spindle, a magnet located in the depression in said base below the yoke and having its poles positioned adjacent to the extreme positions of the movable contact member, cooperating contact members selectively engaged by the movable contact member, and a handle member, normally frictionally held against movement by no the base, for regulating the initial tension of the spring.

2. In combination, in an electric switch, a. base of electric-insulating material, having an opening therethrough and a depression in one surface thereof, a supporting member extending through said opening and frictionally held therein, an adjustable yoke member of substantially U-shape, having one end secured to said support and located in said depression, a spindle pivotally supported between the arms of said yoke member, a bimetallic spring having one end connected to the yoke and the other end to the spindle, a counterbalanced movable contact 12 member carried by the spindle, a magnet located in the depression in said base below the yoke and having its poles positioned adjacent to the extreme positions of the movable contact member, a contact member on said base, a connector bar operatively engaging said contact member and having a portion located in said depression and in frictional engagement With said yoke, cooperating contact members selectively engaged by the movable contact member, and a handle member secured to said supporting member at the front of said base for adjusting the initial tension of said bimetallic spring.

In testimony whereof, I have hereunto sub- 10 scribed my name this 1921.

17th day of January,

BENJAMIN H. SMITH. 

